This application is based on Patent Application No. 2000-143852 filed May 16, 2000 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet recording apparatus which ejects ink from a print head onto a recording sheet to record an image or the like, and more specifically to an ink jet recording apparatus and an ink jet print head which have a status detection function to detect a state of the print head or, in more specific terms, a state of the ink in the print head.
2. Description of the Related Art
Recording apparatus with functions of printer, copying machine and facsimile, combination type recording apparatus including computers and word processors, and recording apparatus used as output devices for work stations are all designed to record an image on a recording sheet, such as paper and plastic thin plate (for OHP, for example), according to image data. Such recording apparatus can be classed into an ink jet type, wire dot type, thermal recording type, thermal imprint type, and laser beam type according to the recording method of the printing means used.
Of these recording methods, the ink jet type recording apparatus (ink jet recording apparatus) ejects ink from the ink jet print head (also referred to simply as a print head) as a printing means onto a recording medium such as a recording sheet to form an image and has the advantage of being able to easily reduce the size of the printing means and print a very fine image at high speed. Other advantages include a low running cost because it can print on plain paper with no special treatment, low noise during printing operation because the ink jet recording apparatus employs a non-impact printing method, and ease with which multicolor inks can be used in forming a color image.
FIG. 24 is a block diagram schematically showing a system configuration in a conventional ink jet recording apparatus.
In the figure, a main controller 11 has a CPU and constitutes a main controller of the ink jet recording apparatus. The main controller 11 converts image data sent from a host computer 10 into pixel data and stores them in a frame memory 12. The main controller 11 also supplies each pixel data stored in the frame memory 12 to a driver controller 17 at a predetermined timing. The driver controller 17 converts the pixel data received into drive data for driving print elements 101 (data for turning on or off the print elements 101 in an ink jet print head board 100). The converted drive data is stored in a drive data RAM 18. According to a control signal output from the main controller 11, the driver controller 17 reads the drive data from the drive data RAM 18 and feed it to a head driver 102 to control the drive timing of the print elements 101.
In the following configuration, the main controller 11 controls the ejection of a conductive ink 50 from the print elements 101 installed in the ink jet print head board 100, the rotation of a carriage feed motor 15 and the rotation of a paper feed motor 16. This control is performed by the main controller 11 controlling the driver controller 17 and motor drivers 13 and 14, thus recording characters and images corresponding to the image data.
The ink jet recording method described above has some ink ejection variations. One such variation is a bubble jet recording method. In this method a heater is installed in each nozzle to impart a thermal energy to the ink in the nozzle to generate a bubble in the ink. The bubble generating energy is used to eject ink from the nozzle. The heater as a print element to generate an energy for ejecting ink may be manufactured by using the semiconductor fabrication process. Hence, the ink jet print head using the bubble jet recording method has the print elements formed on a print head board, which is made from a silicon substrate and bonded with a top plate. The top plate, which is made of resin, such as polysulfone, and glass, is formed with grooves serving as ink passages.
Taking advantage of the fact that the print head board is made from a silicon substrate, not only the print elements but also other functional components are formed on the print head board. The functional components include, for example, a driver for driving the print elements, a temperature sensor used to control the print elements according to the temperature of the print head, and a drive controller for the temperature sensor.
Japanese Patent Application Laying-open No 7-256883 discloses an example of the ink jet print head board described above. The construction of the conventional ink jet print head board disclosed in the above official gazette is shown in FIG. 25.
In FIG. 25, on the ink jet print head board 100 (simply referred to as a board) are arranged heaters 101 as print elements that apply an ink ejection thermal energy to the ink. Power transistors (driver elements) 102 are connected to the parallelly arranged heaters (print elements) 101 to drive the heaters 101.
Also formed on the board 100 are a shift register 104, a latch circuit 103, and a plurality of AND gates 115. The shift register 104 receives image data from outside through a terminal 106 in synchronism with a serial clock received from a terminal 105, and holds image data representing one line.
The latch circuit 103 latches the image data for one line parallelly output from the shift register 104 in synchronism with a latch clock (latch signal) received through a terminal 107, and transfers the image data parallelly to the power transistors 102. The AND gates 115 are provided in one-to-one relationship with the power transistors 102 and apply output signals of the latch circuit 103 to the power transistors 102 in response to an external enable signal.
Denoted 108 is a drive pulse width input (heat pulse) terminal which receives from outside the print head a signal for controlling an ON time of the power transistors 102 as drive elements, i.e., the time during which to apply current to the heaters 101. Designated 109 is a terminal for inputting a drive power (5V) for logic circuits such as the latch circuit 103 and shift register 104. The board 100 also has a ground terminal 110 and terminals 112 for driving a sensor 114 and for a monitor. The terminals 105-112 formed on the board 100 are input terminals to receive the image data and various signals from outside.
Also formed on the print head board 100 is a sensor 114 such as a temperature sensor for measuring the temperature of the print head board 100 and a resistance sensor for measuring a resistance of each heater 101. The head having the driver, temperature sensor and their driving controller all formed on the print head board has already been put to practical use, contributing to improving the reliability of the print head and to reducing the size of the recording apparatus.
In this construction, the image data entered as a serial signal is converted into a parallel signal by the shift register 104, and the converted image data is held in the latch circuit 103 in synchronism with the latch clock. In this state, when a drive pulse signal for the heaters 101 (enable signal for the AND gates 115) is entered through the input terminal 108, the power transistors 102 are turned on according to the image data. Electric current flows to those heaters 101 that correspond to the turned-on power transistors 102, causing these heaters 101 to generate a thermal energy.
The print head board 100 is bonded with the top plate to form liquid passages (or nozzles) for ejecting ink and a common liquid chamber communicating with the liquid passages. In this construction, the ink accommodated in the ink tank (or ink container) is supplied through the common liquid chamber to the nozzles. The thermal energy generated by the heaters as they are driven, as described above, heats the ink in the liquid passages (nozzles) and eject it in the form of ink droplets from ejection ports at the tips of the nozzles.
One of important requirements to ensure stable printing is that the ink always exists stably in the common liquid chamber and in each nozzle. That is, when the amount of ink in the ink tank is running low, when air mixes into the nozzles from the nozzle tips, or when bubbles in the common liquid chamber move into the nozzles, it is difficult to eject ink stably, leading to a possible degradation of printing quality.
Consider a case, for example, where some particular nozzles in the ink jet print head fail to eject ink stably. In this case, portions in a printed image where the printing is not performed normally by these failed nozzles appear as distinguishable lines. Further, when the ink in the common liquid chamber is running low, the ink may not be supplied to some nozzles. In that case, too, these nozzles fail to eject ink, degrading the printing quality.
To detect the occurrence of a partial ink ejection failure with some nozzles in the print head, a method has been proposed for detecting the state of the ink, or more specifically the presence or absence of the ink, in the common liquid chamber and nozzles.
Japanese Patent Application Laying-open No. 58-118267, for example, proposes a method for detecting the presence or absence of ink in each of the nozzles arranged in the ink jet print head. With this method, to detect the presence or absence of ink in each nozzle, a temperature detection element whose resistance changes according to heat is installed in each nozzle in addition to the print element. When the ink in the nozzle runs out, the rate of temperature increase near the nozzle becomes large due to the heat of the heater as the print element. The rate of temperature increase is measured by the temperature detection element to detect the presence or absence of ink.
In the construction disclosed in the Japanese Patent Application Laying-open No. 58-118267, a temperature detection element or sensor needs to be installed in each nozzle to be able to check the temperature near the nozzle. It is also necessary to install either in each nozzle or on the print head board a drive element for driving the temperature detection element or sensor. Such a construction can effectively be applied to a print head which has a relatively large nozzle size and in which the nozzles are arranged with a relatively low density.
In recent years, however, a faster and finer recording is being called for. To meet this demand, efforts are being made every year to achieve a higher printing density by increasing the number of nozzles arranged in the ink jet print head and arranging the nozzles at an increased density.
In the ink jet print head board with such densely arrayed nozzles, it is becoming harder to install in or around the nozzles the temperature detection elements or sensors that correspond to the print elements. Arranging on the board the drive elements for driving the temperature detection elements or sensors is also getting more difficult. The same can be said of the case where the number of nozzles is increased. That is, increasing the number of nozzles arranged on the board results in an increase in the number of elements, which in turn leads to an increased size of the chip on the ink jet print head board or to multiple layers of wiring for electrically connecting the sensor elements and other circuits. This in turn complicates the structure on the board and increases the cost of chip manufacture.
The Japanese Patent Application Laying-open No. 58-118267 does not describe the structure of a detection terminal that electrically connects each temperature detection element to the outside of the head. If the detection terminals provided one for each print element are to be arranged on the board, the total number of terminals required of the head increases. This arrangement also increases not only the number of wires of a flexible board used to electrically connect the head to the recording apparatus but also the number of devices on the recording apparatus body for individually controlling signals to be fed to these wires. Providing the detection terminals on the board therefore leads to an increased size of various parts of the apparatus, making it difficult to avoid a cost increase.
Further, because the construction disclosed in the Japanese Patent Application Laying-open No. 58-118267 employs a temperature change detection technique, the printing methods that can apply this detection technique is limited to those which use the thermal energy generating heaters as the print elements.
It is an object of the present invention to provide an ink jet recording apparatus of a simple construction which can detect ink in the print head with high accuracy.
In one aspect, this invention provides an ink jet recording apparatus having an ink jet print head board mounted on an ink jet print head, the ink jet print head ejecting a conductive ink from ejection ports to perform printing, the ink jet print head board comprising: print elements to supply an energy for ejecting the ink; drive elements to drive the print elements; an insulating protective film formed to cover wires connecting the print elements and the drive elements; a detection electrode capable of detecting, through the ink on the ink jet print head board, a voltage change between signal sources and the drive elements which is produced as the print elements are driven; a periodical drive means to drive the print elements at a predetermined drive frequency; a voltage detection means to periodically detect an output voltage of the detection electrode at a timing corresponding to the drive frequency; and a state check means to check a state of the ink jet print head according to a result of the detection by the voltage detection means.
The impedance of the ink may be set to a constant, lowest value in a frequency band higher than a predetermined frequency. In that case, the periodical drive means preferably drives the print elements at a frequency corresponding to the frequency characteristic of the conductive ink.
The ink state check means may determine whether or not a sufficient amount of the ink to enable appropriate ink ejection is supplied to the ink jet print head board by checking whether the detected voltage output from the voltage detection means is higher than a predetermined voltage value.
In another aspect, this invention provides an ink jet print head which includes: an ink jet print head board; and a top plate combined with the ink jet print head board to form nozzles each corresponding to a predetermined number of the print elements.
In the invention having the construction described above, when a state detection instruction is entered, the print head board drives the print elements at a frequency within a frequency band in which the ink impedance is small. This causes the detected voltage to be output from the detection electrode through the ink present on the ink jet print head board. The value of the detected voltage varies greatly depending on whether there is ink or not. The voltage detection means samples the value of the detected voltage at a timing corresponding to the drive frequency and performs the ink state detection according to the voltage value obtained. This allows the voltage detection to be performed while avoiding noise that occurs periodically according to the drive frequency. Based on the detected voltage, the state check means checks the ink state. Hence, the value of the detected voltage output from the detection electrode changes greatly according to the amount of ink supplied. Because it does not contain noise, the detected voltage value has a good signal-to-noise ratio. Therefore, the state of the print head, more specifically the ink state in the print head, can be detected based on the voltage value with an excellent precision.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.